1. Field of the Invention
The present invention is directed to a magnetic resonance tomography apparatus of the type having a device for motion correction and to a method for motion correction in a magnetic resonance exposure in an angiography procedure with magnetic resonance-monitored vessel intervention. In particular, the present invention is directed to a magnetic resonance tomography apparatus and method wherein, an angiography procedure, a medical intervention device can be introduced into the vessel system and monitored with by magnetic resonance as to its location within the vessel system, and to thereby corrects for movements of the patient such as respiratory motion.
2. Description of the Prior Art
As a medical diagnostic modality, nuclear magnetic resonance tomography has also proven well-suited in order to implement an angiography procedure, a registration of a vessel system, and, in particular, to monitor the introduction of a medical examination device such as, for example, a catheter into a blood vessel. It is distinguished by an especially high contrast resolution for soft tissue and, in particular, allows fluids such as blood and other body fluids to be clearly distinguished relative to other tissue. Good registration of a vessel system thus is possible. The good presentation a vessel system that is already established can be further improved by introducing a contrast agent into the vessel system before the exposure (contrast agent-supported MR angiography [ceMRA]). Registration of the vessels or of the vessel tree of a specific region presented in an overview is referred to as “road map”.
U.S. Pat. No. 5,792,056 discloses a magnetic resonance tomography apparatus with which an angiography procedure is implemented. A vessel intervention occurs by means of an infusion device which administers a contrast agent into the subject to be examined. As a result, a contrast-supported registration of the vessel-system is generated.
Similar to conventional angiography with other examination methods such as directed x-ray exposure or CT, an overview exposure, a road map, is initially also produced in the case of nuclear magnetic resonance tomography, to register the vessel tree that is then graphically presented. The medical examination (intervention) device is then imaged onto the road map, this being introduced into the vessel. The medical examination device is usually a guide wire with a catheter. The two exposures are subsequently overlaid on one another. The problem can occur that the first exposure, the road map, no longer corresponds to the current condition and position of the vessel system, since modifications and distortions of the vessel system occur both due to gross movements on the part of the patient but primarily due to respiratory motion. It can then no longer be reliable whether the medical examination device is still located within a vessel or whether the vessel wall has been perforated, since the catheter and/or guide wire at least sporadically produce the impression in the superimposed exposure that they are located outside the vessel tree. Such a perforation of the vessel wall is a complication that is definitely possible and must be taken very seriously in an interventional vessel operation. It is therefore desirable to avoid such a misrepresentation. The described problem occurs not only when probing or catheterizing smaller vessels wherein the vessel diameter lies on the order of magnitude of the medical intervention device (for example, catheter or guide wire) but also occurs in interventions in larger vessels, since the medical intervention devices do not necessarily lie in the center of the vessel cross-section, but have the tendency to conform to the vessel wall and to be guided thereby when advanced farther into the vessel. The movements of the vessel system can arise from a large variety of sources, such as peristaltics of the intestines and respiration. The latter leads to considerable movements of the vessel system in the region of thorax and parts of the abdomen.
U.S. Pat. No. 5,427,101 discloses a method for correcting image errors that have occurred due to motion (for example due to respiration or heart motion) of the subject being examined. In order to correct these image errors, images that belong to different motion segments are iteratively replaced by new images from which the motion has been calculated out with an algorithm (for example DVA—diminishing variance algorithm).